Ceramic whiteware compositions comprising a borate flux

ABSTRACT

FLUX FOR CERAMIC COMPOSITIONS HAVING 30-60% B2O3, 20-60% SIO2, 5-30% CAO AND/OR MGO AND 0-15% NA2O.

United States Patent 3,704,146 CERAMIC WHITEWARE COMPOSITIONS COMPRISING A BORATE FLUX Joseph Dulat, Fetcham, England, assignor to United States Borax & Chemical Corporation, Los Angeles, Calif. No Drawing. Filed Dec. 2, 1969, Ser. No. 881,577 Claims priority, application Great Britain, Dec. 3, 1968, 57,372/ 68 Int. Cl. C04b 33/00 US. Cl. 106-45 1 Claim ABSTRACT OF THE DISCLOSURE Flux for ceramic compositions having 30-60% B 0 20-60% SiO 5-30% CaO and/or MgO and 0-15% N320.

This invention relates to fluxes for ceramic compositions of the type comprising (a) clay, (b) flint, and (c) a flux. From a ceramic composition of this type are made by firing the composition, the shaped bodies known as white-ware, such as porcelain, pottery and earthenware.

In ceramic compositions of the type hereinbefore defined, the clay is normally a mixture of ball clay and china clay, and the flint may be finely powdered silica, generally calcined. The flux is included in the composition to make it possible to fire the composition successfully at a lower temperature; conventional fluxes include stone (e. g. Cornish Stone), feldspar and nepheline syenite.

A description of certain compositions of the type hereinbefore defined is to be found in the Encyclopaedia of Chemical Technology (Kirk-Othmer) volume 3 (1954), pages 545-574, published by the Interscience Encyclopaedia, in an article entitled Ceramics (White-Ware).

We have now discovered a novel flux for a ceramic composition, comprising a ground frit having an analysis, in terms of oxides: SiO 2060%; B O 30-60%; CaO and/ or MgO--530%; and Na O-O-%. All parts and percentages in this specification are by weight.

The invention includes not only this flux, but also a method of forming it which comprises (1) forming a mixture of compounds containing oxygen, silicon and calcium and/or magnesium, and optionally sodium, such that the mixture has an analysis, in terms of oxides, as defined above, (2) heating the mixture until a homogeneous melt is formed and then cooling the melt, and (3) grinding the cooled mixture.

The invention extends also to a ceramic composition comprising (a) clay, (b) flint and (c) a flux, in which component (c) is the novel flux. Further, the invention embraces a ceramic composition comprising (a) clay, (b) flint and (c) a flux, in which component (c) is the novel flux together with another flux. The invention also embraces a ceramic body formed by firing one of the present compositions and to such a body which has been glazed.

Where the novel flux is used together with a conventional flux, there is, of course, usually less conventional flux than standard practice would require. When the flux is a mixture of the novel flux and another flux, the other flux usually constitutes at most one-half, and often at most one-third of the total flux.

In general, when the novel flux replaces stone, it is found that a smaller proportion than of the replaced stone is needed. For example, a composition may require 15 parts of stone to give a desired result in the fired body, while the corresponding composition may require only 5 parts of the novel flux of this invention.

Although the novel flux may have no sodium content, it is preferred that the Na O analysis be about 5-10%.

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Possible Preferred NazO 0-15 5-10 CaO and/or MgO 5-30 10-20 B203--." 30-60 4045 S102 20-60 25-35 In the present preparation of the novel flux, a mixture of the appropriate starting materials is first formed. The starting materials are usually in the form of powders and usually are thoroughly mixed. The next step is to heat until a homogeneous melt is formed. When the mixture of materials is heated to a temperature above the melting point of the lower-melting ingredients such as boric oxide (45 C.) or calcium borate, the higher-melting ingredients such as lime, magnesia or silica begin to dissolve in the molten ingredient, forming a complex of indeterminate structure but of the same oxide analysis as the starting materials. The mixture should be heated to such a temperature that it is entirely liquid so that the individual components can be intimately intermixed and any reaction between the components takes place freely. Thus the initial mixture must be heated to a temperature which is within the melting range of the cooled melt. When calcium in the form of its oxide is to be present in the flux then a temperature of at least 1,000 C., usually of the order of l,l00 C., is generally necessary, the exact temperature being dependent upon the proportions of the respective ingredients, and when magnesium in the form of its oxide is to be in the fiux rather higher temperatures may be needed.

The starting materials can be any which result in a satisfactory fiux. It is especially preferred, however, that the silicon content be provided in the form of silica precipitated from a silica sol. Since the preparation of the flux involves the production of a homogeneous melt, a wide choice of borates may be employed as starting material. At least part of the calcium and boron may be provided in the form of calcium borate (2CaO-3B O At least part of the sodium and boron may be provided in the form of borax, Na B O -10H O, or anhydrous sodium tetraborate. Another convenient starting material is ulexite, NaCaB O -8H O, thereby providing Na O, CaO and E 0 Calcium borate even in the form of a relatively crude ore (providing it is free from excessive amounts of objectionable contaminants, particularly iron) can be employed, as can low-value ores of calcium borosilicates such as howlite and datolite. Magnesium borate and calcium magnesium borate may also be employed. Calcium and magnesium can also be supplied in the hydroxide or oxide. Often a mixture of a calcium borate and calcium hydroxide are included. A preferred combination is calcium or magnuesium hydroxide, oxide, or borate, silica, and a sodium borate, such as anhydrous sodium tetraborate, or boric acid.

The 20-60% SiO content in the novel flux has a notable beneficial effect on the strength of the ceramic bodies which can be produced. The flux is particularly advantageous since a lower proportion of it can usually result in an earthenware body at least equivalent to an earthenware body containing a higher proportion of a conventional flux. Thus, the flux whose analysis, in terms of oxides, is in the ranges 510% Na O, 10-20% CaO, 40-45% B 0 and 33% SiO used at 5 parts per parts of a standard clay/flint mixture is equivalent, and in some respects superior, to a conventional flux used at 15 parts per 85 parts of the standard clay/ flint mixture; this is demonstrated hereinafter.

4 A further advantage of the novel flux is that it results 25 parts ball clay: Parts by weight in an optimum firing temperature often about 50 C. Vitblend 343 ball clay lower than normally required. Furthermore, lower density B.W.S. ball clay 5 bodies with comparable and sometimes superior strength E.W.V.A. ball clay (pH value 5.1) 5 compared to that of conventional bodies can usually be 5 E.O.B.C. ball clay (pH value 5.2) 5 made with the new flux. In addition, the new flux can Fayles blue ball clay 5 readily be controlled to provide uniformity in composi- S.C. china clay (pH value 4.5) 12 /2 tion and quality, together with flexibility which enables C.C. china clay (pH value 4.5) 12 /2 the composition to be varied to suit specific needs. Flint 35 The novel flux is generally present to the extent of less than of the ceramic composition, such as 1-10% 10 ,522 352 2 5zig zg g gfig hgi s g gisg 1 and preferably 3-525, by weight. plastic consistency.

The invention 18 illustrated by the following example. Each mixture was then passed through a pug mm, made EXAMPLE into /2 inch diameter rods approximately 6 inches in 5 length from which ovoids were rolled by hand. Each rod and ovoid was marked and numbered for future reference.

(a) Preparation of fluxes (c) Firing of bodies The materials used to prepare the fluxes, and the quantities of the material employed, are shown in Table I Ten rods, four ovoids and two deformation pieces of below. each body were placed in an oven at 110 C. to dry, after TABLE I Weight of materials taken in preparing the fluxes Analyses of the fluxes, percent Calcium borate Boric Anhydrous Calcium Flux Code No. ore oxide borax hydroxide Silica NazO (3210 B203 SiO:

24 s50 112-5 97.5 119.1 150 6.7 40 33.3 A sea. 192 150 150 10.3 11.7 44.7 33.3

The stated quantities of materials were weighed out, which they were put into a kiln and fired at 50 C./hour thoroughly mixed by hand, placed in a graphite crucible with a 2 hour soak at peak. and introduced into a gas-fired furnace; this was brought Four firings were done for each body, namely at 1,050 slowly to 1,200 C. at which temperature the mixture had C., 1,080 C., 1,100" O, and 1,150 C.

3 255; S fi; $2 $25 3 2: if i g gi fi g g (d) Determination of physical properties of bodies water. The mixture was recovered, placed in an evapo- Properties of the bodies after firing are shown in the rating dish and put into an electric oven at 110 C. to following Tables 11 and 1H.

TABLE IL-PHYSICAL PROPERTIES OF BODIES AFTER FIRING Body Properties 24 S A S50 SE Firln tern erature, C- 1, 050 1, 080 1, 100 1, 150 1,050 1, 080 1, 100 1, 150 1, 030 1, 060 1, 080 1, 150 1, 200 Appa ent gorosity, percen 21.1 21. 5 17. 9 11. 2 18. 1 13. 0 10. 1 4. 6 29. 4 26. 23. 2 12. 4 5. 2 Water absorption, percent 12.5 10. 9 8.6 5. 2 8. 4 5. 9 4. 5 2. 1 16.0 13.7 11. 7 5. 6 2. 3 Bulk density, g./0u. 1n 1. 86 1. 91 2. 00 2.05 1. 92 2. 03 2. 12 2. 20 1. 82 1. 90 1. 99 2. 20 29 Dry-fired volume shrinkage, percent 18. 2 18. 8 21. 7 26. 0 15. 1 17. 9 24. 6 23. 8 3. 9 8. 2 11. 8 20. 2 24. 0 Linear shrinkage, percent 6. 5 6. 8 7. 8 9. 5 5. 3 6. 4 9.0 12. 4 13 2. 8 4. 1 7. 2 8. 7 Deformation, degrees- 12 13 12 14 12 11 12. 5 2. 5 4 4 8 14 Modulus of rupture, lbsJs 5, 640 6, 090 7, 080 7, 720 6, 140 5, 800 8, 330 9, 500 2, 560 3, 700 4, 750 7, 980 8, 830 C or G C C G C C W G W W W W 0 Surface texture S S S R S S S R S S S S S NoTEs.-W=Whito; C Creamish; G Graylsh; S Smooth; R Rough; not determined.

dry. When dry, the mixture was placed in a porcelain ball mill charged with steel balls and milled for 16 hours (overnight). The following morning the resultant powder The apparent porosity was measured as follows. A n was passed through a 200 mesh British Standard sieve. A ovoid was weighed dry and then evacuated for 1 hour 1n magnet was finally passed through the powder to pick a vacuum desiccator down to a pressure of 3 cm. of merup any ion filings. cury or less. Distilled water, which in the meantime had been boiled and cooled rapidly in cold water in order to (b) Preparation of bodles remove dissolved air, was admitted to the desiccator. When one y was P p from each flux y mixing 35 the air had ceased to come off from the pieces, the vac- Pafts of Standard y mix with 5 Parts of fillX- For uum was broken, the beaker containing the ovoidsinwater Comparative P p a Standard earthenware y was removed, and boiled for 20 minutes. They were then noted J made y mixing 35 Pdrts of Standard body allowed to soak for at least 4 hours but preferably overmiX with 15 Parts of Stone was also P P night. The ovoids were then weighed, suspended, using a The mix used in Preparing these bodles was Prepared bridge on the balance. The surplus water was then refrom five different ball clays and two different china clays, moved from the ovoids with a damp cloth and weighed for purpose of experiment; plainly one might use a single clay of each ype. The mix used had the following compositions:

If the weight of the dry test piece=A g. If the weight of the suspended test piece=B g.

If the weight of the soaked test piece=C g.

then apparently porosity=g:% x 100% The water absorption was calculated from the results above as being A T x 100% The dry-fired shrinkage was determined as follows. When calcuating the bulk density, the bulk volume had to be determined. The difference between the bulk volumes of green and fired body is the volume shrinkage, which can be expressed as a percentage on the dry bulk volume basis.

The linear shrinkage was derived from the volume shrinkage by the formula:

Where a percent linear shrinkage c=percent cubic shrinkage.

The deformation was determined by the method described by Edwards and Holdridge in Trans. Brit. Ceram. Soc., 63, 249, 1964. The test piece was formed from a dry rod by inserting it into the jig, and scraping down the exposed sides with a razor. Two of these test pieces for each suitable body were made, being supported in a refractory base at an angle of 45. This set-up was placed in the kiln, together with the rods and ovoids. After firing and cooling the angle through which these test pieces have bent is expressed as the angle of deformation.

The modulus of rupture was determined as follows. Rods dried at 110 C. were placed between the knife edges, which were 4 inches apart, of a modulus of rupture machine. A constant rate of load was applied, this being 200 lbs/min.

Modulus of rupture= where l=span (in); w=1oad (lbs); d=diameter of rod (in.)

Average of results on rods was taken as the reading.

TABLE III.THERMAL EXPANSION OF FIRED BODIES Firlng Thermal expansion, percent Body with temp.,

flux Code No. C. 20500 C. 20-560 C. 20650 C. 20770 C.

The thermal expansion was measured in a standard thermal expansion machine. The test piece, in the form of a rod, was about 3 inches long. This was placed in the tube and the rod brought into contact with it, so that one end was against the end of the tube, while the other end was in contact with the rod. The slight pressure of the spring in the dial gauge ensured that contact between the test piece and the rod was maintained throughout the experiment. The furnace temperature rose at a rate of 30 C./5 min. readings being taken every 30 C.

On the balance of properties, the optimum firing temperature of the standard earthenware body is in the region of 1,150 C. It can be seen from the properties recorded above in Table II that the closest fit with the properties of the standard body fired at 1,150" C. occurs for the test bodies fired at 1,100 C. Thus the optimum firing temperature of the test bodies is about 50 C. lower than that of the standard body.

Another advantage of the test bodies which can be seen from Table II is their lower bulk densities than that of the standard body. This enables a body of the same volume to be made with lesser material if the present compositions rather than a standard composition are employed.

I claim:

1. A composition for firing into a white-ware ceramic body consisting essentially of about 25 parts of ball clay, about 25 parts of china clay, about 35 parts of flint, and about 5 parts of a previously melted and solidified, finely divided flux consisting essentially of Percent SiO 25-35 B 0 40-45 Na O 5-10 CaO and/ or MgO 10-20 said parts by weight.

References Cited UNITED STATES PATENTS 2,155,721 4/1939 Lee 106-54 2,233,575 3/ 1941 Bair 10645 2,511,679 6/1950 Thiess 10654 2,776,899 1/1957 Donahey 10645 2,782,126 2/ 1957 Butler et al. 10646 2,862,827 12/ 1958 Boyce et al 10654 X 3,413,133 11/1968 Stalego 10654 X 2,466,849 4/ 1949 Hood 10654 2,693,668 11/ 1954 Slayter 10654 2,839,414 6/1958 Fenity et al 10646 3,019,116 1/1962 Doucette 10646 OTHER REFERENCES Latimer, W. M. et al.: Reference Book of Inorganic Chemistry, New York, 1951, pp. 325-6.

TOBIAS E. LEVOW, Primary Examiner W. R. SATTERFIELD, Assistant Examiner U.S. c1. X11. 10654, 313

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION I Patent No. 3:7 1A6 D d November 28 1972 Inventor(s) Joseph Dulat It is certified that error appears in the aboveident ified patent and that said Letters Patent are hereby corrected as shown below:

In Column 3, line 6%, delete "ion filings" and insert -iron filings-;

line 30, delete "112-5" insert --ll2.5--.

In Column 5, line 11, the word "calcuating should read --calculating--.

Singed and sealed this 22nd day of May 1973.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attes'ting Officer Commissioner of Patents F ORM PO-IOSO (10-69) USCOMM-DC sows-Pas i [1.5. GOVERNMENT PRINTING OFFICE I969 O36G-334 

